1. Field of the Invention:
The present invention relates to a sensing apparatus and method based on the use of Raman spectroscopy.
2. Description of the Prior Art:
Raman spectroscopy is a well established technique and the Raman spectra of a multitude of chemical elements and compounds are documented in the literature. A sensing device which makes use of Raman spectroscopy to detect the presence of a particular species in a medium is disclosed in U.S. Pat. No. 4, 781,458. This prior device comprises an optical fibre with a light transmissive fibre optic core within a generally opaque cladding, save that over a portion of the fibre the cladding is removed and the exposed core has a coating of a metal. This metal is one which enhances emission of Raman signals of substances adsorbed thereon. The apparatus further comprises a light source and a detector for detecting Raman signals.
In use of this prior apparatus, that portion of the fibre optic core which is coated with the metal is placed in a medium (usually a liquid) in which it is desired to test for the presence of particular species. These species become adsorbed on the metal. Light is shone along the fibre and passes through the thin metal coating. The adsorbed species produce Raman signals which are emitted in all direction, some propagating along the fibre and being detected by the detector. The spectra obtained is characteristic of the adsorbed species, and the intensity of the spectra is indicative of the concentration of the species in the medium.